That gives only a 509 Ohm reactance at 1800 Pete. Going to an oft suggested
100uH raises that to 1131 which is possibly sufficient. I use 220uH for a
2488 XL simply because I have a bunch from a hamfest and they work fine for
me in similar service.
Carl
KM1H
----- Original Message -----
From: "Pete Smith N4ZR" <n4zr@contesting.com>
To: "topband reflector" <Topband@contesting.com>
Sent: Wednesday, January 22, 2014 3:32 PM
Subject: Topband: Buffaloed by a bias tee
I'm still wrestling with the bias tee for my 1-of-8 remote beverage
switch. If I use a cliplead to connect a 270-ohm dummy load, bypassing
the relay, and connect an MFJ-259B to the receiver port on the controller,
the impedance looks completely reasonable - with a 3:1 binocular
transformer, 89 ohms R and X=5, measured by the MFJ. However, as soon as
I connect a 12V regulated supply to the bias tee - one of the little radio
shack variable wallwarts - the measured R drops to 5 ohms and the X goes
up to 19.
My history major's diagnosis is inadequate isolation between the DC supply
and the RFline, but why? The series RF choke in the DC line is 7 turns on
a ferrite core, measures 45 uH at 2 MHZ, and the bypass capacitor is a
0.01 uF disk, on thesupply side of the choke. Theseries cap between the
Antenna and the RX jacks on the controller is a .1 uF disk (it was what I
had). I do not yet have a safety choke between the RX side and ground,
but will add one before I deploy it, if I can ever figure out what's going
on.
I'd really appreciate some ideas of what to try. Thanks in advance!
--
73, Pete N4ZR
Check out the Reverse Beacon Network at
http://reversebeacon.net,
blog at reversebeacon.blogspot.com.
For spots, please go to your favorite
ARC V6 or VE7CC DX cluster node.
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